script.aculo.us provides you with easy-to-use, cross-browser user interface JavaScript libraries to make your web sites and web applications fly.
script.aculo.us is a set of JavaScript libraries to enhance the user interface of web sites. It provides an visual effects engine, a drag and drop library (including sortable lists), a couple of controls (Ajax-based autocompletion, in-place editing, sliders) and more.

Visual effects
There are five core effects script.aculo.us offers: Opacity, Scale, MoveBy, Highlight, and Parallel. Through these effects there are over 16 additional effects using combinations of the core effects out of the box. Programmers can also extend and make new effects.